Longitudinally adjustable reversible axial piston machine

ABSTRACT

The invention relates to a reversible axial piston machine ( 1 ) consisting of a cylinder drum ( 5 ) which rotates about a rotational axis ( 7 ) and in which pistons can be displaced in cylinders ( 6 ), said pistons being supported against an inclined surface ( 8 ). The angle of adjustment (α 1, α2 ) of the inclined surface ( 8 ) can be adjusted in both pivoting directions by means of a control piston ( 24 ) pertaining to the adjusting device ( 12 ), said control piston extending essentially parallel to the direction of the rotational axis ( 7 ) of the cylinder drum ( 5 ). The zero position of the adjustment of the inclined surface ( 8 ) can be adjusted without play by means of a zero position adjusting device ( 32 ).

The invention relates to a reversible axial piston machine having anadjusting device for adjusting the pivot angle of a pivot balance of thereversible axial piston machine in both pivotal directions.

The volume of hydraulic fluid delivered in a rotation of the drive shaftof an axial piston machine is dependent on the stroke length of thecylinders arranged in a cylinder drum of an axial piston machine duringa compression or suction procedure. The stroke length is set by inclinedpoints of the inclined surface of a pivot balance, on which theindividual cylinders are supported during their rotational movementabout the drive axis, in relation to the axial alignment of the driveaxis. The control angle of the inclined surface with respect to theaxial alignment of the drive axis is adjusted by an adjusting device.

For axial piston machines which are operated in both pivotaldirections—reversible axial piston machines—positive and negativeadjustment angles have to be set at the pivot balances.

In principle, there are two embodiments for the arrangement of theadjusting device in relation to the arrangement of the drive axis of theaxial piston machine. In the case of transverse adjustment, theadjusting device executes a translatory movement for adjusting the pivotbalance transversely to the arrangement of the drive axis of the axialpiston machine. In the case of longitudinal adjustment, the adjustingdevice executes a translatory movement for adjusting the pivot balancein the longitudinal direction of the drive axis of the axial pistonmachine. When taking into account structural considerations—for examplewhen using the axial piston machine in mobile concretemixers—longitudinal adjustment is preferred over transverse adjustmentsince this has a smaller overall volume.

A not insignificant problem with adjusting devices is the precisesetting of the zero position. If, in the uncontrolled operatingcondition of the adjusting device, no control pressure is applied forexample to a pressure-controlled adjusting device (unpressurisedoperating condition), the adjustment angle of the pivot balance isprecisely zero degrees when the set zero position of the adjustingdevice is set correctly. In this case, the inclined surface is preciselyperpendicular to the longitudinal axis of the drive shaft. None of thepistons in any of the cylinders of the cylinder drum is able to executea stroke movement here.

DE 37 14 888 A1 illustrates a reversible axial piston machine having anadjusting device which operates according to the variant withlongitudinal adjustment. The zero position of the pivot balance in theuncontrolled operation of the axial piston machine is non-adjustable andis undefined. In this axial piston machine, the adjustment angle whichis actually set at the pivot balance does not, therefore, generallycorrespond precisely to the predetermined adjustment angle. The actualdisplacement volume therefore generally deviates from the predetermineddisplacement volume.

The object of the invention, therefore, is to further develop thereversible axial piston machine with longitudinal adjustment accordingto the features in the precharacterising clause of claim 1 in such a waythat there is definitely no presence of displacement volume in theuncontrolled condition.

The object of the invention is achieved by a reversible axial pistonmachine having the features of claim 1.

According to the invention, to set the zero position in the pivotbalance, a zero-position setting device is provided in the adjustingdevice according to claim 1. The advantage of this zero-position settingdevice is that the zero position of the inclined surface can be setprecisely and without play in the uncontrolled operation of the axialpiston machine.

Advantageous, and particularly detailed, constructions of the inventionare described in the dependent claims.

A further advantage of the zero-position setting device can be seen inthe use of a single pressure spring which is tensioned between twospring plates on the adjusting rod and acts on the control piston, whichis displaceable in the adjusting device, in both control directions withthe same pretension force. In the adjustment procedure for determiningthe zero position, it is thus possible to position the control piston,and the pivot balance which is coupled to the control piston by way of aform-fitting attachment, in both control or pivotal directions by meansof a pretension force defined by the spring constant of the pressurespring. This means that there is no need to carry out a complexprocedure for ensuring that the spring constants, and therefore thepretension forces, of two opposingly acting pressure springs, which inapplications of this type normally each generate a pretension force forone adjusting device, are equally matched.

The claimed reversible axial piston machine and the associated adjustingdevice is furthermore advantageous in that the adjustment travel of thecontrol piston or the adjustment angle of the pivot balance can beadjustably delimited by way of a second adjusting rod, which is likewiseguided out of the adjusting device or the axial piston machine.

Finally, the claimed adjusting device is advantageous in that, owing toits hollow cylindrical construction, the control piston, thezero-position setting device and other components located within thehollow cylinder of the adjusting device can be assembled and dismantledin relatively simple manner.

An exemplary embodiment of the invention is illustrated in the drawingand will be described in more detail below. The drawing shows:

FIG. 1 a cross-sectional illustration of an axial piston machineaccording to the invention, with an adjusting device according to theinvention;

FIG. 2 a cross-sectional illustration of an adjusting device accordingto the invention;

FIG. 3 a cross-sectional illustration of a further embodiment of theadjusting device according to the invention; and

FIG. 4 a three-dimensional view of an axial piston machine according tothe invention, with an adjusting device according to the inventionconnected by way of a form-fitting attachment.

The reversible axial piston machine according to the invention and theadjusting device according to the invention are described in both theirembodiments below with reference to FIG. 1 to FIG. 4.

FIG. 1 shows a cross-section of a reversible axial piston machine 1according to the invention. This comprises a drive shaft 4 mounted in anaxially aligned cutout 2 of the housing 3. Arranged in rotationallyfixed manner on the drive shaft 4, there is a cylinder drum 5 in which aplurality of cylinder cutouts are arranged at equal mutual spacings fromone another on a circle which is concentric with the longitudinal axis 7of the drive shaft 4.

Displaceably guided in each of the cylinder cutouts, there is a piston 6which has, on its end opposite the cylinder chamber, a spherical headwhich is pivotably mounted in a guide shoe and supported against aninclined surface 8.

In relation to a zero-position axis 10, which is aligned at a rightangle to the axis of rotation 7 of the cylinder drum 5, the pivotbalance 9, and with it the inclined surface 8, is pivotable through apositive adjustment angle α1 and negative adjustment angle α2 withrespect to the zero-position axis 10.

The adjusting device 12, whereof the cross-section—in addition to theillustration in FIG. 1—is also illustrated on a slightly enlarged scalein FIG. 2, comprises a hollow cylinder 13 which serves as a housing andhas a first step 14. The first opening 15 in the hollow cylinder 13,which faces the pivot balance 9, is not closed and enables a controlpiston 16 guided in the hollow cylinder 13 to be displaced at leastpartially out of the inner region 17 of the hollow cylinder 13. Thesecond opening 18 of the hollow cylinder 13, which is opposite the firstopening 15, is closed by a closing cover 19.

The closing cover 19 has an annular web 20. The external diameter of theannular web 20 of the closing cover 19 corresponds to the internaldiameter of the hollow cylinder in the region between the first step 14and the second opening 18. The internal diameter of the annular web 20of the closing cover 19 corresponds to the internal diameter of thehollow cylinder 13 in the region between the first step 14 and the firstopening 15. The closing cover 19 is guided into the interior 17 of thehollow cylinder 13 by means of an annular web 20 in such a way that aform-fitting connection is produced between the hollow cylinder 13 andthe closing cover 19.

Incorporated in the inner lateral surface 21 of the hollow cylinder 13,between the first opening 15 and the first step 14, and also in theinner lateral surface 27 of the annular web 20 of the closing cover 19,there are annular grooves 22 in which guide rings 23, for example ofbrass, are arranged. These guide rings 23 serve as guide bearings forthe control piston 24, which is mounted centrically to the longitudinalaxis 11 in the interior 17 of the hollow cylinder 13 and is displaceablein the direction of the longitudinal axis 11.

The control piston 24 has a substantially hollow cylindrical geometry.At approximately half the cylinder height of the hollow cylindricalcontrol piston 24, the control piston 24 has a flange-like widening 26on its outer lateral surface 25. Since the width of this flange-likewidening 26 corresponds to the width of the first step 14 of the hollowcylinder 13, the flange-like widening 26 of the control piston 24 is incontact with the inner lateral surface 27 of the hollow cylinder 13between the first step 14 and the second opening 18.

The geometry of the control piston 24, the hollow cylinder 13 and theclosing cover 19 in the region of the flange-like widening 26 of thecontrol piston 24 results in the formation of a first control pressurechamber 28 and a second control pressure chamber 29 in the interior 17of the hollow cylinder 13. The first side face 30 of the flange-likewidening 26 of the control piston 24, which is connected to the firstcontrol pressure chamber 28, serves as a working surface for a controlpressure which is guided through the first control pressure opening 31in the wall of the hollow cylinder 13 and into the first controlpressure chamber 28 for the purpose of displacing the control piston 24along its longitudinal axis 11 in the direction of the second opening 18of the hollow cylinder 13. The second side face 32 of the flange-likewidening 26 of the control piston 24, which is connected to the secondcontrol pressure chamber 29, serves as a working surface for a controlpressure which is guided through the second control pressure opening 33in the wall of the hollow cylinder 13 and into the second controlpressure chamber 29 for the purpose of displacing the control piston 24along its longitudinal axis 32 in the direction of the first opening 15of the hollow cylinder 13.

To seal the first and second control pressure chambers 28 and 29 againsthydraulic fluid, sealing rings 36 which are guided in grooves areprovided in the region of the inner lateral surfaces 21 and 27 of thehollow cylinder 13, the inner lateral surface 22 and the outer lateralsurface 34 of the annular web 20 of the closing cover 19 and the endface 35 of the flange-like widening 26 of the control piston 24.

The hollow cylindrical control piston 24 has a multi-stepped cutout 37whereof the largest third opening 38 faces in the direction of thesecond opening 18 of the hollow cylinder 13. A first adjusting rod 39 isguided along the longitudinal axis 11 of the control piston 24 into themulti-stepped cutout 37. This first adjusting rod 39 is guided out ofthe adjusting device 12 by way of a bore 40 in the closing cover 19. Byspecifically screwing an adjusting nut 41 on the thread of the adjustingrod 39 outside the closing cover 19, the first adjusting rod 39 can beadjustably positioned in the adjusting device 12, in the cavity 17 ofthe hollow cylinder 13 or in the cutout 37 of the control piston 24.

Fixed on the adjusting rod 39 in the region between the second step 42and the third opening 38 of the cutout 37 of the control piston 24,there is a first spring plate 43 and a second spring plate 44. The firstspring plate 43 is fixed on the adjusting rod 39 in that the pretensionforce of a pressure spring assembly 45 tensioned between the firstspring plate 43 and the second spring plate 44 presses the spring plate43 against the inside end face 46 of a closing flange 47 fixed to theinternal hollow cylinder end of the adjusting rod 39. The second springplate 44 is fixed on the adjusting rod 39 in that the pretension forceof the pressure spring assembly 45 presses the spring plate 44 against asleeve 48 fixed between the spring plate 44 and the closing cover 19 onthe adjusting rod 39. The sleeve 48 has, on its inside, an annulargroove in which an annular body 55 is fixed, which is arranged in agroove of the first adjusting rod 39 and is supported against the insideend face 46a of the groove arranged in the adjusting rod 39. The sleeve48 and the position of the groove arranged in the adjusting rod couldalso be constructed according to a further embodiment illustrated inFIG. 3 so that the spring plate 44 is pressed directly against theannular body 55. In the exemplary embodiment, the pressure springassembly 45 is composed of the two parallel-arranged pressure springs45A and 45B, so that a compact construction can be achieved with thepressure spring assembly 45.

In addition to being fixed to the adjusting rod 39, a first spring plate43 is in contact with the second step 42 of the cutout 37 of the controlpiston 24 by means of its end face 49 which is remote from the pressurespring assembly 45. By means of its end face 50 which is remote from thepressure spring assembly 45, the second spring plate 44 is in contactwith a snap ring 51 arranged in the vicinity of the third opening 38 inan annular groove on the inner side face of the cutout 37 of the controlpiston 24.

A second adjusting rod 52, which is guided into the interior 17 of thehollow cylinder 13 by way of a bore 53 in the closing cover 19, servesas an adjustable delimitation for the adjustment travel of the controlpiston 24 along its longitudinal axis 32. The position of the secondadjusting rod 52 within the interior 17 of the hollow cylinder 13 can bealtered by screwing an adjusting nut 54 in defined manner on the threadof the second adjusting rod 52 outside the closing cover 19.

The pivot balance 19 is adjusted in the direction of a positiveadjustment angle al to effect a zero-point adjustment by positioning thefirst adjusting rod 39 in the direction of the second opening 18 of thehollow cylinder 13 by means of actuating the first adjusting screw 41.The zero-point setting device 32, comprising the first adjusting rod 19,the pressure spring assembly 45, the first spring plate 43, the secondspring plate 44 and the sleeve 48, is thus displaced in the direction ofthe second opening 18 of the hollow cylinder 13. The force required forthis displacement is transmitted from the closing flange 47 of theadjusting rod 39, which is moved in the direction of the second opening18 of the hollow cylinder 13, by way of its inside end face 46 to thefirst spring plate 43, from the first spring plate 43 to the pressurespring assembly 45, from the pressure spring assembly 45 to the secondspring plate 44 and finally from the second spring plate 44 to the snapring 51 which, fixed with form fit to the control piston 24, displacesthe control piston 24 in the direction of the second opening 18.

The pivot balance 19 is adjusted in the direction of a negativeadjustment angle α2 to effect a zero-point adjustment by positioning thefirst adjusting rod 39 in the direction of the first opening 15 of thehollow cylinder 13 by means of actuating the first adjusting screw 41.The zero-point setting device 32 is thus displaced in the direction ofthe first opening 15 of the hollow cylinder 13. In this case, the forceis transmitted from the sleeve 48, which is moved by way of the annularbody 55 with the first adjusting rod 39 in the direction of the firstopening 15 of the hollow cylinder 13, to the second spring plate 44,from the second spring plate 44 to the pressure spring assembly 45, fromthe pressure spring assembly 45 to the first spring plate 43 and finallyfrom the first spring plate 43 to the second step 42 of the cutout 37 ofthe control piston 24. The transmission of the force to the controlpiston 24 effects a displacement of the control piston 24 in thedirection of the first opening 15 of the hollow cylinder 13.

In addition to the damped force transmission from the first adjustingrod 39 to the control piston 24 within the framework of the zero-pointadjustment of the pivot balance 9, the predominant task of the pressurespring assembly 45 is that of generating a spring force which isproportional to the excursion of the control piston 24 and whichcounteracts the control force triggering the movement. This restoringspring force is identical for both displacement directions of thecontrol piston 24 owing to the use of a single pressure spring assembly45. The spring force of the pressure spring assembly 45 also has adefined value in the zero position of the pivot balance 9 since thepressure spring assembly 45 is held pretensioned between the firstspring plate 43 and the second spring plate 44 in each of the positionsof the control piston 24.

If the control pressure which is guided through the first controlpressure opening 31 into the first control pressure chamber 28 and actson the first side wall 30, serving as the working surface, of theflange-like widening 26 is greater than the control pressure which isguided through the second control pressure opening 33 into the secondcontrol pressure chamber 29 and acts on the second side wall 32, servingas the working surface, of the flange-like widening 26, then the controlpiston 24 is displaced in the direction of the second opening 18 of thehollow cylinder 13. As a result of the displacement of the controlpiston 24 in the direction of the second opening 18 of the hollowcylinder 13, the first spring plate 43 is subjected to a force at itsend face 49 from the second step 42 of the hollow cylinder 13, whichforce is transmitted by way of the pressure spring assembly 45 to thesecond spring plate 44 and results in a displacement of the secondspring plate in the direction of the second opening 18 of the hollowcylinder 13. The second spring plate 44 lies with its end face 50against the sleeve 48 and, due to the adjusting rod 39 being fixedlocally and to the sleeve 48, is not displaceable in the direction ofthe second opening of the hollow cylinder 13. In this case, a furtherincrease in the control pressure in the first control pressure chamber28 results in an additional compression of the pressure spring assembly45 and therefore in an additional increase in the spring force, which isproportional to the further increase in the control pressure. Thisensures a steady displacement of the control piston 24 in the adjustingdevice 12, which is proportional to the control pressure differencebetween the first control pressure chamber 28 and the second controlpressure chamber 29.

If the control pressure guided into the first control pressure chamber28 is lower than the control pressure guided into the second pressurechamber 29, the control piston 24 is displaced in the direction of thefirst opening 15 of the hollow cylinder 13. By way of the displacementof the control piston 24, and therefore the snap ring 51 integrated inthe control piston 24, in the direction of the first opening 15 of thehollow cylinder 13, a force is transmitted to the second spring plate44, which is in turn transmitted from the second spring plate 44 to thepressure spring assembly 45. Since the first spring plate 43 always lieswith its end face 49 against the second step 46 of the cutout 37 of thecontrol piston 24, the compression of the pressure spring 45 assemblywhen there is a negative control pressure difference between the firstcontrol pressure chamber 28 and the second control pressure 29 isproportional to the increase in the control pressure difference. Thisensures a steady increase in the spring force, which is proportional tothe control pressure difference between the first control pressurechamber 28 and the second pressure chamber 29, and therefore aproportional displacement of the control piston 24 in the adjustingdevice 12.

According to FIG. 4, the axial movement of the control piston 24 alongits longitudinal axis 11 is converted into a pivotal movement of thepivot balance 9 by way of a slide block 56 which is guided in a groove57 of the adjusting device 12. The slide block 56 has a cutout (notillustrated in FIG. 4), in which a journal (not illustrated in FIG. 4)is rotatably mounted. This journal is mounted on the side face of aconnecting arm 58, which is in turn fixed to the pivot balance 9. Theone-dimensional axial movement of the control piston 24 in the adjustingdevice 12 is consequently converted into a rotary pivotal movement ofthe pivot balance 9 by way of a one-dimensional sliding movement of theslide block 56 in the groove 57 of the adjusting device 12 incombination with a rotary movement of the journal in the cutout of theslide block 56.

1. A reversible axial piston machine having a cylinder drum whichrotates about an axis of rotation and in the cylinder cutouts of whichpistons, which are supported against an inclined surface, are movable,the control angle (α1, α2) of said inclined surface being adjustable byan adjusting device, the adjusting device having a control piston whichadjusts the control angle (α1, α2) in both pivotal directions andextends with a substantial direction component parallel to the directionof the axis of rotation of the cylinder drum, wherein the zero positionof the inclined surface, in which the inclined surface is orientedperpendicularly to the axis of rotation of the cylinder drum, can be setwithout play by a zero-position setting device.
 2. A reversible axialpiston machine according to claim 1, wherein the zero-position settingdevice comprises a first adjusting rod which is positionably guided in astepped cutout of the control piston, said cutout extending in thedirection of the longitudinal axis of the control piston, and positionsthe control piston in the two directions of its longitudinal axis.
 3. Areversible axial piston machine according to claim 1, wherein theinclined surface is constructed on a rotatably mounted pivot balance. 4.A reversible axial piston machine according to claim 2, wherein thecontrol piston is guided in a hollow cylinder which has a first step onits inside and whereof the first opening, which is oriented in thedirection of the inclined surface, is not closed in order to also enablean axial movement of the control piston outside the hollow cylinder, andwhereof the second opening, which is oriented away from the pivotbalance, is closed by a closing cover.
 5. A reversible axial pistonmachine according to claim 4, wherein the position of the firstadjusting rod outside the adjusting device is set by the first adjustingrod being guided out of the hollow cylinder of the adjusting device byway of the closing cover.
 6. A reversible axial piston machine accordingto claim 4, wherein the control piston is positioned in one of the twodirections of the longitudinal axis of the control piston by arespective first and second spring plate which is each fixed on thefirst adjusting rod.
 7. A reversible axial piston machine according toclaim 6, wherein the first spring plate is fixed on the first adjustingrod in that the first spring plate is pressed against the inside endface of a closing flange by the spring force of at least onepretensioned pressure spring located between the first and second springplate 3, 4, said closing flange being mounted on that end of the firstadjusting rod which is located inside the hollow cylinder of theadjusting device.
 8. A reversible axial piston machine according toclaim 7, wherein the second spring plate is fixed on the first adjustingrod in that the second spring plate is pressed against a sleeve by thespring force of the pretensioned pressure spring, said sleeve beingguided between the second spring plate and the closing cover on theadjusting rod.
 9. A reversible axial piston machine according to claim6, wherein the control piston is positioned in the direction of thefirst opening of the hollow cylinder in that the first spring plate ispressed against the end face of a second step of the cutout of thecontrol piston as a result of the first adjusting rod being positionedin the direction of the first opening of the hollow cylinder.
 10. Areversible axial piston machine according to claim 6, wherein thecontrol piston is positioned in the direction of the second opening ofthe hollow cylinder in that the second spring plate is pressed against asnap ring as a result of the first adjusting rod being positioned in thedirection of the second opening of the hollow cylinder, said snap ringbeing guided in an annular groove along the side face of the cutout ofthe control piston in the region of the third opening of the cutout. 11.A reversible axial piston machine according to claim 4, wherein theclosing cover has an annular web whereof the external diametercorresponds to the internal diameter of the hollow cylinder from thesecond opening to the first step of the hollow cylinder, and whereof theinternal diameter corresponds to the internal diameter of the hollowcylinder from the first step to the first opening of the hollowcylinder.
 12. A reversible axial piston machine according to claim 11,wherein the closing cover is guided in the second opening of the hollowcylinder by means of its tubular web in such a way that a cavity isproduced between the hollow cylinder, the closing cover and the controlpiston and, at the same time, the control piston is mounted on the innerside wall of the annular web of the closing cover and the inner sidewall of the hollow cylinder between the first step and the first openingof the hollow cylinder.
 13. A reversible axial piston machine accordingto claim 12, wherein the control piston has, on its lateral surface inthe region of the cavity, a widening which reaches to the inner sidewall of the hollow cylinder and divides the cavity into a first controlpressure chamber and a second control pressure chamber.
 14. A reversibleaxial piston machine according to claim 13, wherein the first and secondcontrol pressure chambers are each supplied with a control pressure byway of a respective control pressure opening in the wall of the hollowcylinder.
 15. A reversible axial piston machine according to claim 13,wherein the two side faces of the widening of the control piston serveas working surfaces for the two control pressures for displacing thecontrol piston in the two directions along the longitudinal axis of thecontrol piston.
 16. A reversible axial piston machine according to claim15, wherein with a defined control pressure, the control piston effectsan equal control angle (α1, α2) of the inclined surface in both pivotaldirections as a result of the working surfaces of the control pistonbeing of equal size.
 17. A reversible axial piston machine according toclaim 3, wherein the control piston, which is axially movable in thedirection of its longitudinal axis, is attached with form fit to thepivot balance by way of a slide block which is mounted in a groove ofthe control piston and has a cutout in which a journal connected to thepivot balance by way of a connecting arm is fixedly mounted.
 18. Areversible axial piston machine according to claim 7, wherein with anequal excursion of the control piston in one of the two directions alongthe longitudinal axis of the control piston, the pressure spring, whichis fixed in the cutout of the control piston on the first adjusting rod,generates an equal restoring force for both directions of the excursionas a result of a defined control pressure.
 19. A reversible axial pistonmachine according to claim 4, wherein the axial excursion of the controlpiston along the longitudinal axis of the control piston is adjustablydelimited by way of a second adjusting rod, which is guided out of thehollow cylinder of the adjusting device by way of the closing cover.